Load meter and load measurement method

ABSTRACT

A load meter includes a detector, a storage unit, and a load calculator. The detector detects, by using a captured image obtained by capturing a road and a vehicle present on the road, a displacement amount in the captured image, the displacement amount corresponding to displacement caused on the road by application of a load of the vehicle. The storage unit stores information indicating a relation between the load and the displacement amount. The load calculator calculates the load based on the displacement amount and the information.

TECHNICAL FIELD

The present disclosure relates to a load meter that measures a load of avehicle or the like.

BACKGROUND ART

Conventionally, a load measuring device that measures a load of avehicle or the like has been known. For example, PTL 1 discloses a loadmeasuring device for measuring a load of a vehicle running on a road.This load measuring device measures the load of the vehicle using a loadsensor embedded in the road.

CITATION LIST Patent Literature

PTL 1: Japanese Patent No. 5424787

SUMMARY

The conventional load measuring device described above needs to embedthe load sensor for measuring the load in the road. Therefore,installment or removal of the conventional load measuring device needs acertain amount of cost and labor.

In view of this, the present disclosure provides a load measuring devicethat can keep labor and cost for installment or removal lower thanconventionally.

A load meter according to one aspect of the present disclosure includesa detector, a storage unit, and a load calculator. The detector detects,by using a captured image obtained by capturing a road and a vehiclepresent on the road, a displacement amount in the captured image, thedisplacement amount corresponding to displacement caused on the road byapplication of a load of the vehicle. The storage unit storesinformation indicating a relation between the load and the displacementamount. The load calculator calculates the load based on thedisplacement amount and the information.

The load measuring device according to the present disclosure can keeplabor and cost for installment or removal lower than conventionally.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view schematically illustrating one example of a state inwhich an axle load is measured according to a first exemplaryembodiment.

FIG. 2 is a block diagram illustrating a configuration of a load meteraccording to the first exemplary embodiment.

FIG. 3 is a configuration table of displacement coefficient data.

FIG. 4A is a flowchart for describing an operation of a firstmeasurement process.

FIG. 4B is a flowchart for describing an operation of a calibrationprocess.

FIG. 5 is a view illustrating one example of captured image A.

FIG. 6 is a view illustrating one example of a captured image.

FIG. 7 is a view illustrating one example of captured image B.

FIG. 8A is a graph illustrating one example of a histogram generated bya calibrator.

FIG. 8B is a graph illustrating one example of a histogram generated bythe calibrator.

FIG. 8C is a graph illustrating one example of a histogram of axle loadvalues acquired in advance.

FIG. 8D is a graph illustrating one example of a histogram generated bya calibrator according to a modified example.

FIG. 9 is a view schematically illustrating one example of a state inwhich an axle load is measured according to a second exemplaryembodiment.

FIG. 10 is a block diagram illustrating a configuration of a load meteraccording to the second exemplary embodiment.

FIG. 11 is a view schematically illustrating one example of a state inwhich an axle load is measured according to a third exemplaryembodiment.

FIG. 12 is a block diagram illustrating a configuration of a load meteraccording to the third exemplary embodiment.

FIG. 13A is a view illustrating one example of patterned light.

FIG. 13B is a view illustrating one example of patterned light.

FIG. 13C is a view illustrating one example of patterned light.

FIG. 13D is a view illustrating one example of patterned light.

FIG. 13E is a view illustrating one example of patterned light.

FIG. 14 is a view schematically illustrating a relation between aprojecting direction of the patterned light and an imaging direction.

FIG. 15A is a view schematically illustrating the patterned light asseen in the imaging direction.

FIG. 15B is a view schematically illustrating the patterned light asseen in the imaging direction.

FIG. 16 is a flowchart for describing an operation of a thirdmeasurement process.

FIG. 17 is a view illustrating one example of captured image A.

FIG. 18 is a view illustrating one example of captured image B.

DESCRIPTION OF EMBODIMENTS

A load meter according to one aspect of an exemplary embodiment includesa detector, a storage unit, and a load calculator. The detector detects,by using a captured image obtained by capturing a road and a vehiclepresent on the road, a displacement amount, in the captured image,corresponding to displacement caused on the road by application of aload of the vehicle. The storage unit stores information indicating arelation between the load and the displacement amount. The loadcalculator calculates the load based on the displacement amount and theinformation.

Accordingly, the load meter can keep labor and cost for installing orremoving the load meter lower than conventionally.

It is to be noted that these generic or specific aspects may beimplemented by using a system, a method, an integrated circuit, acomputer program, or a computer-readable recording medium such as acompact disc read only memory (CD-ROM), and may also be implemented byany combination of the system, the method, the integrated circuit, thecomputer program, and the recording medium.

A specific example of the load meter according to one aspect of thepresent disclosure will be described below. It should be noted that eachof the exemplary embodiments described hereafter illustrates onepreferred specific example of the present disclosure. Numerical values,shapes, materials, components, arrangement positions and connectionconfigurations of the components, steps, processing order of the steps,and the like shown in the following exemplary embodiments are mereexamples, and are not intended to limit the present disclosure. Thepresent disclosure is limited only by the scope of the claims.Accordingly, among the components in the following exemplaryembodiments, components that are not described in any of independentclaims indicating the most generic concept of the present disclosure arenot essential for achieving the object of the present disclosure but aredescribed as preferable components.

First Exemplary Embodiment

As one aspect of the present disclosure, a load measuring systeminstalled in a road on which ordinary vehicles travel will be describedherein.

It is assumed herein that a calibration device is operated by beingincorporated in a load meter that constitutes the load measuring system.The load meter and the calibration device according to the presentdisclosure will be described below with reference to the drawings.

[1-1. Configuration]

FIG. 1 is a view schematically illustrating one example of a state inwhich load meter 200 according to a first exemplary embodiment measuresan axle load of vehicle 102. As illustrated in FIG. 1 , load measuringsystem 1 according to the first exemplary embodiment includes imagingdevice 101 and load meter 200.

Herein, for example, load meter 200 is connected to imaging device 101for capturing an image of road 103 on which vehicle 102 travels.Moreover, a plurality of captured images of road 103 captured by imagingdevice 101 is input to load meter 200. Load meter 200 uses the inputcaptured images, thereby calibrating a displacement coefficient to beused when the axle load of vehicle 102 is calculated. For example,vehicle 102 is a truck, and road 103 is an asphalt road.

FIG. 2 is a block diagram illustrating a configuration of load meter200. As illustrated in FIG. 2 , load meter 200 includes input unit 210,axle load calculator 240, and calibration device 300. Calibration device300 includes axle identifying unit 220, speed calculator 230, calibrator250, detector 260, storage unit 270, and notification unit 280. Inaddition, detector 260 includes axle load position identifying unit 261and displacement amount detector 262. Calibration device 300 is acalibration device for calibrating load meter 200 that measures an axleload of a vehicle.

For example, load meter 200 is implemented in such a way that amicroprocessor (not illustrated) in a computer (not illustrated)provided with the microprocessor and a memory (not illustrated) executesa program stored in the memory.

Input unit 210 receives an input of the plurality of captured images ofthe road captured by imaging device 101. Herein, input unit 210, forexample, receives an input of a digital image with 4096 pixels×2160pixels as the captured image. Input unit 210 outputs the receivedcaptured images to axle identifying unit 220, speed calculator 230, axleload position identifying unit 261, and displacement amount detector262.

The captured images are input through wireless or wired communication orthrough a recording medium.

Detector 260 detects, at a predetermined point, a displacement amountcorresponding to displacement caused on a road surface of a road when avehicle passes.

When a vehicle is included in the captured image received by input unit210, axle load position identifying unit 261 identifies an axle loadposition of the vehicle in the captured image. More specifically, axleload position identifying unit 261 performs image recognition processingon the captured image to determine whether or not the vehicle isincluded in the captured image. Then, when the vehicle is included inthe captured image, axle load position identifying unit 261 recognizes atire of the vehicle by further image recognition processing. Axle loadposition identifying unit 261 then identifies an area on the road, whichcorresponds to a lowermost point of the tire, as an axle load position.Axle load position identifying unit 261 outputs the identified axle loadposition to calibrator 250 and displacement amount detector 262.

Displacement amount detector 262 detects, by using the captured imagereceived by input unit 210, a displacement amount, in the capturedimage, corresponding to displacement caused on the road when an axleload is applied. Particularly, when the axle load position is input fromaxle load position identifying unit 261, displacement amount detector262 detects a displacement amount corresponding to displacement at theidentified axle load position. By comparing a captured image in which nodisplacement is caused on the road and a captured image in whichdisplacement is caused on the road, from among the plurality of capturedimages received by input unit 210, displacement amount detector 262detects a displacement amount corresponding to the displacement.Displacement amount detector 262 can detect a displacement amountbetween the captured images by using block matching, a correlationmethod, or an optical flow. For example, displacement amount detector262 calculates, as the displacement amount, the number of pixels thatindicates a difference in pixel positions corresponding to an identicalpoint on the road between the captured images. Further, the capturedimage in which no displacement is caused on the road may be a capturedimage in which the road is captured in advance in a state in which thevehicle is not present, a captured image in which an image change amountis less than or equal to a certain level among a plurality of capturedimages of the road captured in succession, or a captured imagedetermined that the vehicle is not present through the image recognitionprocessing.

When the vehicle is included in the captured image received by inputunit 210, axle identifying unit 220 identifies where the axle of thevehicle in the captured image is located as viewed from a front (or arear) of the series of axels. More specifically, axle identifying unit220 performs the image recognition processing on the captured image todetermine whether or not the vehicle is included in the captured image.Then, when the vehicle is included in the captured image, axleidentifying unit 220 recognizes the axle of the vehicle by further imagerecognition processing. Axle identifying unit 220 then identifies anaxle number from the front for each vehicle. Axle identifying unit 220outputs the identified axle number to calibrator 250. Here, asillustrated in FIG. 1 , axle identifying unit 220, for example,identifies a forefront axle of vehicle 102 as first axle 10. Further,axle identifying unit 220, for example, identifies a subsequent axle assecond axle 20.

When the vehicle is included in the captured image received by inputunit 210, speed calculator 230 calculates a speed of the vehicle. Morespecifically, speed calculator 230 performs the image recognitionprocessing on the captured image to determine whether or not the vehicleis included in the captured image. Then, speed calculator 230 calculatesthe speed of the vehicle based on a difference in positions of anidentical vehicle between different frames (for example, betweenadjacent frames). By previously measuring a positional relationshipbetween imaging device 101 and the road, speed calculator 230 cangeometrically perform scale conversion between a movement amount in thecaptured image and an actual movement amount. Speed calculator 230outputs the calculated speed to calibrator 250.

Calibrator 250 aggregates the displacement amounts detected by detector260 to generate a histogram of the displacement amounts. Then,calibrator 250 updates a displacement coefficient based on a shape ofthe histogram of the displacement amounts.

Calibrator 250 aggregates the displacement amounts detected by detector260 for the plurality of captured images in which different vehicles arecaptured. Particularly, when the axle load position is identified byaxle load position identifying unit 261, calibrator 250 aggregates thedisplacement amounts by associating the identified axle load positionand the displacement amount with each other. Similarly, calibrator 250aggregates the displacement amounts by dividing the displacement amountsfor each axle number identified by axle identifying unit 220 and foreach speed calculated by speed calculator 230. For example, calibrator250 aggregates the displacement amounts by dividing the displacementamounts for the first axle and the second axle. Further, calibrator 250,for example, aggregates the displacement amounts by dividing thedisplacement amounts for a low speed (for example, 0 km/h to 30 km/h), amedium speed (for example, 30 km/h to 60 km/h), a high speed (forexample, 60 km/h or more), and the like. Calibrator 250 may aggregatethe displacement amounts by combining all the conditions, or mayaggregate the displacement amounts by combining only a part of theconditions. Further, calibrator 250 may aggregate the displacementamounts by combining only the condition, such as the first axle (theforemost axle of the vehicle), and the condition, such as 30 km/h ormore. By dividing (or limiting) the conditions, calibrator 250 caneasily obtain a characteristic of the histogram of the displacementamounts, which will be described below.

Storage unit 270 stores first information indicating a relation betweenthe axle load and the displacement amount. More specifically, the firstinformation is a relational equation indicating the relation between theaxle load and the displacement amount when the displacement is caused onthe road due to application of the axle load to the road, and adisplacement coefficient used for this relational equation. Storage unit270 may be implemented by a memory (not illustrated) included in loadmeter 200 or a database of an external device capable of performingcommunication.

Axle load w (kg) is a function of displacement amount d (the number ofpixels). In other words, axle load w is represented by an equation ofw=f(d) using function f. Herein, function f is handled after beingapproximated with a linear equation. Accordingly, storage unit 270stores the linear equation (w=αd) as the relational equation. Further,storage unit 270 stores coefficient α as the displacement coefficient.

This displacement coefficient α has a displacement coefficient valueassociated with each of a plurality of positions that can be identifiedas an axle load position by axle load position identifying unit 261.With this configuration, differences including a difference in distancesfrom imaging device 101 to the axle load position, a difference incompositions of a material such as asphalt, a difference in road surfacetemperatures, and a difference in deterioration states of the roadsurface can be reflected on displacement coefficient α for each area onthe road. Herein, displacement coefficient α has, for each area(hereinafter written as “local area”) of 10 pixels in a horizontaldirection (x direction) and 10 pixels in a vertical direction (ydirection), for example, in the captured image, a displacementcoefficient value corresponding to the local area.

FIG. 3 is a table illustrating one example of displacement coefficient αstored in storage unit 270.

Storage unit 270 stores a predetermined relational equation and apredetermined displacement coefficient in an initial state. When adisplacement coefficient is newly calculated by calibrator 250, thestored displacement coefficient is updated by the newly calculateddisplacement coefficient.

Axle load calculator 240 calculates an axle load of a vehicle present onthe road based on the displacement amount detected by detector 260 andthe first information stored in storage unit 270. Particularly, when theaxle load position is identified by axle load position identifying unit261, axle load calculator 240 calculates the axle load based on thedisplacement amount at the identified axle load position. Morespecifically, axle load calculator 240 calculates axle load w bymultiplying displacement amount d detected by displacement amountdetector 262 by a displacement coefficient value corresponding to anarea including the axle load position identified by axle load positionidentifying unit 261. Further, storage unit 270 may store the axlenumber identified by axle identifying unit 220 and the displacementcoefficient according to the speed calculated by speed calculator 230.Moreover, axle load calculator 240 may calculate an axle load by usingthe axle number of the vehicle and the displacement coefficientaccording to the speed.

Further, storage unit 270 stores second information pertaining to theaxle load. The second information is an axle load value of the firstaxle of the vehicle of which a traffic frequency is expected to behighest in road 103.

Calibrator 250 calculates a displacement coefficient for identifying arelation between the axle load and the displacement amount based on thedisplacement amount detected by detector 260 and the second information.Then, calibrator 250 updates the displacement coefficient stored instorage unit 270 by using the calculated displacement coefficient. Adetail of a method for calculating the displacement coefficient will bedescribed in a calibration process, which will be described below.

When a difference between the displacement coefficient newly calculatedby calibrator 250 and the first information is a predetermined referencevalue or more, notification unit 280 notifies the outside of the systemof this situation. For example, after notification unit 280 notifies anexternal user through wired or wireless communication, calibrator 250may update the displacement coefficient based on a judgment of the user.

An operation of load meter 200 (particularly calibrator 250) having theabove configuration will be described with reference to the drawingshereafter.

[1-2. Operation]

Load meter 200 performs, as its characteristic operation, a firstmeasurement process and the calibration process.

[1-2-1. First Measurement Process]

The first measurement process is a process, when a captured imageincluding a vehicle is input to load meter 200, for calculating an axleload of the vehicle.

FIG. 4A is a flowchart for describing an operation of the firstmeasurement process. This first measurement process is started when thecaptured image including the vehicle (hereinafter written as “capturedimage A”) is input to input unit 210.

When the first measurement process is started, input unit 210 acquirescaptured image A input from imaging device 101 (step S10).

FIG. 5 is a view illustrating one example of captured image A acquired.As illustrated in FIG. 5 , captured image A includes vehicle 102traveling on road 103. Also, this vehicle 102 is in contact with road103 at lowermost point 410 of a tire of vehicle 102. Further, in FIG. 5, area 420 includes a point that is not identified as an axle loadposition.

In FIG. 4A, upon the acquisition of captured image A, axle load positionidentifying unit 261 performs image recognition processing to identifylowermost point 410 of the tire of vehicle 102. Then, axle load positionidentifying unit 261 identifies an area on road 103, which correspondsto identified lowermost point 410, as the axle load position (step S20).

Herein, the area identified by axle load position identifying unit 261may not necessarily be an area consisting only of one point (one pixel).The area identified by axle load position identifying unit 261 may be alocal image area consisting of a plurality of adjacent pixels. It is tobe noted that axle load position identifying unit 261 may limit an axleload detection range in which an axle load is detected to an area ofroad 103. Further, axle load position identifying unit 261 may limit theaxle load detection range in which the axle load is detected to a partof road 103, as in area 510 in FIG. 6 . Axle load position identifyingunit 261 may limit the detection range according to designation of auser, or may limit the detection range according to the designation ofthe user and a result of image recognition of a color or a texture ofroad 103. Limiting the axle load detection range provides an effect ofreducing an image processing amount. Therefore, the image processingamount for identifying the axle load position can be reduced. It is tobe noted that, when a plurality of tires is in contact with road 103 inthe captured image, axle load position identifying unit 261 identifieseach contact position as the axle load position.

Upon the identification of the axle load position, displacement amountdetector 262 detects a displacement amount corresponding to displacementcaused at the identified axle load position on road 103 (step S30).Displacement amount detector 262 detects a displacement amount by usingcaptured image A and a captured image in which no displacement is caused(hereinafter written as “captured image B”) from among the capturedimages acquired by input unit 210. If captured image B has not beenacquired by input unit 210 before the axle load position is identified,displacement amount detector 262 waits until captured image B isacquired by input unit 210, and then detects the displacement amount.

FIG. 7 is one example of captured image B acquired. Road 103 is imagedfrom an identical point of view in captured image A (see FIG. 5 ) andcaptured image B. Area 610 on road 103 in captured image B is an areaidentical to the area on road 103, which corresponds to lowermost point410 of the tire, in captured image A. Further, area 620 on road 103 incaptured image B is an area identical to area 420 on road 103 incaptured image A.

Displacement amount detector 262 detects a displacement amount causedbetween an area on road 103, which corresponds to lowermost point 410,in captured image A, and area 610 in captured image B. Herein, since adisplacement amount on road 103 caused by an axle load of an ordinaryvehicle is very small, it is desirable to suppress an effect of shake ofimaging device 101 due to vibration or the like of the vehicle travelingon road 103. As one example, displacement amount detector 262 selects,in both captured image A and captured image B, an identical point thatis not identified as the axle load position (for example, area 420 incaptured image A and area 620 in captured image B). Then, displacementamount detector 262 calculates a displacement amount between theselected areas (hereinafter written as a “non-axle load positiondisplacement amount”). Displacement amount detector 262 subtracts thisnon-axle load position displacement amount from a displacement amountcaused between the area on road 103, which corresponds to lowermostpoint 410 of the tire, in captured image A, and area 610 in capturedimage B. Accordingly, displacement amount detector 262 corrects thedisplacement amount. Thus, the effect of the shake of imaging device 101can be suppressed. Besides, the effect of the shake of imaging device101 can be also suppressed by a method using an optical imagestabilization technology, a method using a mechanical mechanism such asa sensor shift method, or the like.

In FIG. 4A, upon the detection of the displacement amount, axle loadcalculator 240 identifies a displacement coefficient value correspondingto the axle load position identified by axle load position identifyingunit 261 (step S40). In other words, axle load calculator 240 refers todisplacement coefficient α stored in storage unit 270 (see FIG. 3 ) toidentify a displacement coefficient value corresponding to the axle loadposition identified by axle load position identifying unit 261.

Upon the identification of the displacement coefficient value, axle loadcalculator 240 multiplies the identified displacement coefficient valueby the displacement amount detected by displacement amount detector 262to calculate an axle load (step S50).

Upon the calculation of the axle load, axle load calculator 240 outputsa numerical value of the calculated axle load to the outside (step S60).Herein, when the numerical value of the calculated axle load is greaterthan a predetermined reference value, axle load calculator 240 maynotify the user of this situation through notification unit 280, insteadof outputting the numerical value of the calculated axle load to theoutside. In this case, the reference value may be an absolute value ormay be a relative value. In addition, for example, when the referencevalue is more than or equal to 30 times a representative value of ahistogram described below, axle load calculator 240 may notify the userof this situation after storing the corresponding captured image. Withthis configuration, the user can be notified of a relatively highpossibility that the vehicle included in the corresponding capturedimage is overloaded.

After the process in step S60 is ended, load meter 200 ends the firstmeasurement process.

[1-2-2. Calibration Process]

The calibration process is a process in which calibrator 250 updates thedisplacement coefficient stored in storage unit 270.

FIG. 4B is a flowchart of the calibration process. This calibrationprocess is started when load meter 200 is activated.

When the calibration process is started, in a case where a load positionis identified by axle load position identifying unit 261, calibrator 250inputs a displacement amount every time the displacement amount isdetected by displacement amount detector 262 (step S110). Similarly,calibrator 250 inputs an axle number from axle identifying unit 220(step S120), and inputs a speed from speed calculator 230 (step S130).Calibrator 250 aggregates displacement amounts by associating thedetected displacement amount with every condition of the identified axleload position, the axle number, and the speed (step S140). Herein,calibrator 250 may not generate a histogram of displacement amounts forcombinations of all the conditions, and may generate a histogram ofdisplacement amounts for only a limited condition, such as a combinationof a specific axle number and a specific speed. It is to be noted thatsteps S110 to S130 may not be provided in this order.

Herein, calibrator 250 aggregates the detected displacement amounts foreach local area associated with the displacement coefficient value.

Load meter 200 repeats the processes in steps S110 to S140 until apredetermined condition is satisfied. Herein, the predeterminedcondition corresponds to, for example, a case where a predetermined datehas come, a case where a predetermined number of displacement amountsare aggregated, or a case where the user performs a predeterminedoperation to load meter 200.

When the predetermined condition is satisfied in the process in stepS150 (Yes in step S150), calibrator 250 generates a histogram ofdisplacement amounts aggregated in a certain period in the past for eachlocal area based on an obtained aggregation result (step S160).

Each of FIGS. 8A and 8B is a diagram illustrating one example of thehistogram generated by calibrator 250 for each local area. In FIGS. 8Aand 8B, vertical axes represent a frequency, and horizontal axesrepresent a displacement amount. The histograms illustrated in FIGS. 8Aand 8B are examples of histograms with mutually different aggregationperiods and classified by an identical local area, an identical axlenumber, and an identical speed. A reason that shapes of these histogramsare different is that road surface temperatures are mutually different,deterioration states of the road surfaces are mutually different, or thelike, in these aggregation periods.

Upon the generation of the histogram for each local area, calibrator 250extracts a characteristic of the histogram (step S170). Then, calibrator250 calculates a displacement coefficient of the corresponding localarea based on the characteristic of the histogram and the secondinformation stored in storage unit 270. Then, calibrator 250 updates thedisplacement coefficient stored in storage unit 270 to the calculateddisplacement coefficient (step S180). Herein, the characteristic of thehistogram indicates a representative value of the displacement amountobtained from the shape of the histogram, such as an average, a mode, amaximum, a minimum, or an average of lower levels with a certainfraction. A case where the mode of the histogram is used as thecharacteristic of the histogram is described herein as one example.

Storage unit 270 stores, as the second information, the axle load valueof the first axle of the vehicle of which the traffic frequency isexpected to be highest in road 103.

Calibrator 250 calculates the displacement coefficient by dividing thesecond information by the mode serving as the representative value ofthe displacement amount obtained from the shape of the histogram.

For example, calibrator 250 calculates displacement coefficient α1 basedon the histogram illustrated in FIG. 8A and the following Equation (1).α1=w1/d1  (1)where the second information is represented by w1, and the mode of thehistogram illustrated in FIG. 8A is represented by d1.

Further, for example, calibrator 250 calculates displacement coefficientα2 based on the histogram illustrated in FIG. 8B and the followingEquation (2).α2=w1/d2  (2)

where the second information is represented by w1, and the mode of thehistogram illustrated in FIG. 8B is represented by d2.

It is to be noted that, if the expected characteristic of the histogramcannot appropriately be obtained, such as the case where precision ofthe histogram is low because of the small number of traveling vehicles(for example, less than or equal to a certain number), calibrator 250may calculate the displacement coefficient by using a substitute valueinstead of the mode. For example, calibrator 250 may use a displacementcoefficient in a past time period, or may continuously use thedisplacement coefficient which has been used before updating thehistogram, as the substitute value.

Further, the histogram of the displacement amounts may have a pluralityof frequency peak values. In this case, calibrator 250 may use anaverage, a mode, a maximum, or a minimum within a certain range of adisplacement amount. With this configuration, a stable characteristic ofthe histogram can be obtained.

It is to be noted that, when displacement coefficient α depends on aspeed of a vehicle, speed calculator 230 calculates speed v of thevehicle from a movement amount of the vehicle in captured images, inwhich road 103 is continuously captured in a time-series manner. Also,calibrator 250 may calculate displacement coefficient α(v) for eachspeed v. Further, calibrator 250 may update the histogram or calculatethe displacement coefficient only when the speed is within a certainrange (for example, when speed v of the vehicle <20 km/h).

In FIG. 4B, after calculating the displacement coefficient, calibrator250 overwrites the displacement coefficient stored in storage unit 270by using the calculated displacement coefficient, thereby updating thedisplacement coefficient (step S180).

After the process in step S180 is ended, load meter 200 proceeds againto the process in step S110, and repeats the processes in step S110 andsubsequent steps.

It is to be noted that calibrator 250 may notify the outside of the needto calibrate the displacement coefficient without automatically updatingthe displacement coefficient. For example, before step S180, calibrator250 notifies a manager on the outside of the system of the need tocalibrate the displacement coefficient by using notification unit 280through wired or wireless communication. Then, after the managerconfirms the notification, calibrator 250 may update the displacementcoefficient. Further, load measuring system 1 may function as a systemthat notifies timing for executing conventional calibration byperforming only notification.

[1-3. Effects Etc.]

As described above, load meter 200 according to the first exemplaryembodiment includes detector 260, storage unit 270, and axle loadcalculator 240. Detector 260 detects, by using captured image A obtainedby capturing road 103 and vehicle 102 present on road 103, adisplacement amount, in captured image A, corresponding to displacementcaused on road 103 by application of an axle load of vehicle 102.Storage unit 270 stores information indicating a relation between theaxle load and the displacement amount. Axle load calculator 240calculates an axle load based on the displacement amount and theinformation.

Further, calibration device 300 detects a displacement amount caused bythe axle load of vehicle 102 traveling on road 103 from the capturedimage captured by external imaging device 101. Calibrator 250 generatesa histogram of the displacement amounts by aggregating the displacementamounts during passage of the plurality of vehicles. Calibrator 250 canupdate a displacement coefficient stored in storage unit 270 by using acharacteristic of this histogram and second information about the axleload recorded in storage unit 270.

Accordingly, when load meter 200 is calibrated, there is no need toperform calibration work by preparing a vehicle whose axle load isknown. Therefore, calibrator 250 can automatically implement calibrationof load measuring system 1.

Further, by selectively generating a histogram for an axle number,calibrator 250 can select an axle that can easily obtain a shapecharacteristic of the histogram. Accordingly, calibration precisionimproves. Further, by selectively generating a histogram for a speed ofthe vehicle, calibrator 250 can select a speed that can easily obtain ashape characteristic of the histogram. Accordingly, calibrationprecision improves.

Further, calibrator 250 may calculate a displacement coefficient basedonly on a shape of a histogram corresponding to a first axle (aforefront axle of the vehicle) as the axle number. For example, it isdifficult to precisely calculate an axle load of an axle other than thefirst axle due to an influence of a load and the like placed on aplatform of the vehicle. On the other hand, a load of an engine of thevehicle is applied to an axle load of the first axle, and the axle loadof the first axle is hardly affected by a weight of the load on theplatform of the vehicle. Accordingly, the axle load of the first axle iscalculated more precisely than the axle load of the other axles.Accordingly, calibrator 250 can precisely calculate a displacementcoefficient by calculating the displacement coefficient based only onthe shape of the histogram corresponding to the first axle.

Further, when displacement is measured using an image, it is desirablethat calibration device 300 calibrate a displacement coefficient foreach position of road 103. With this configuration, multipointcalibration can be easily implemented by automatic calibration.Accordingly, cost and labor for maintenance and management of themeasuring system can be reduced.

Further, even when the calibration is not performed automatically,calibration device 300 can automatically detect timing to be calibrated.Accordingly, updating work can be performed in a necessary andsufficient frequency.

The displacement coefficient for calculating the axle load of thevehicle is corrected in the present exemplary embodiment. However, adisplacement coefficient for calculating a load of a vehicle may becorrected. A load meter previously records a relation between the loadof the vehicle and an axle load of the vehicle. The load meter cancalculate the load of the vehicle by measuring the axle load of thevehicle. As with load meter 200, this load meter generates a histogramof displacement amounts, and updates a displacement coefficient forcalculating the load of the vehicle based on a shape of the histogram.

The load meter measures the axle load of the vehicle in the presentexemplary embodiment. However, a load meter may measure a load of anentire vehicle in an area where the entire vehicle is placed. In thiscase, a detector detects displacement amounts at positions of aplurality of axles, and calculates an average of the displacementamounts. As with load meter 200, this load meter generates a histogramof the averages of the displacement amounts, and updates a displacementcoefficient for calculating the load of the vehicle based on a shape ofthe histogram.

Further, storage unit 270 may record a histogram of loads or axle loadsof a vehicle traveling on a road. Moreover, calibrator 250 may update adisplacement coefficient based on a shape of a histogram of displacementamounts and a shape of the histogram of the loads or the axle loads ofthe vehicle.

[1-4. Modified Example]

A load meter according to a modified example will be described withreference to FIGS. 8C and 8D. It is to be noted that the load meteraccording to the modified example has a configuration similar to theconfiguration of above-described load meter 200.

FIG. 8C is a graph illustrating one example of a histogram of loadvalues acquired in advance. More specifically, the histogram in FIG. 8Cis generated by using a calibrated load sensor or load meter. In thepresent modified example, storage unit 270 stores information indicatingthis histogram.

In the histogram in FIG. 8C, a mode of output values is frequency s3.The histogram in FIG. 8C has three peak values (frequency s4, frequencys5, and frequency s6) other than frequency s3.

FIG. 8D is a graph illustrating one example of a histogram ofdisplacement amounts generated by calibrator 250. The histogram in FIG.8D is generated from captured images of a road at a position closer to aposition of the road in which the above-described load sensor isinstalled. In other words, the histogram in FIG. 8C corresponds to thehistogram in FIG. 8D.

In the histogram in FIG. 8D, a mode of the displacement amounts isfrequency d3. The histogram in FIG. 8D has three peak values (frequencyd4, frequency d5, and frequency d6) other than frequency d3. Herein, asillustrated in FIGS. 8C and 8D, it is considered that frequency s3corresponds to frequency d3. Similarly, it is considered that frequencys4, frequency s5, and frequency s6 respectively correspond to frequencyd4, frequency d5, and frequency d6.

Calibrator 250 of calibration device 300 in the present modified exampleupdates a displacement coefficient based on shapes of the histogram inFIG. 8C and the histogram in FIG. 8D. Specifically, calibrator 250calculates the displacement coefficient such that axle load values atfrequencies s3 to s6 in FIG. 8C substantially coincide with axle loadvalues corresponding to the displacement amounts at frequencies d3 to d6in FIG. 8D, respectively. With this configuration, calibrator 250 canupdate the displacement coefficient by using the highly reliableexisting histograms generated by measuring axles of many vehicles.Further, calibrator 250 can calculate the displacement coefficient moreprecisely by using characteristics of the plurality of histograms (thatis, the peak values of the plurality of histograms).

It is to be noted that, upon the calculation of the displacementcoefficient, calibrator 250 may not use frequency s3 and frequency d3serving as the modes. In the present modified example, a vehiclecorresponding to the mode of the histogram is a vehicle having a lightaxle load. When the light axle load is measured, an error easily occursin the measurement of the axle load. Accordingly, frequency s3 andfrequency d3 serving as the modes easily include many errors. Because ofthis, calibrator 250 can precisely calculate the displacementcoefficient by not using frequency s3 and frequency d3. As describedabove, calibrator 250 may update the displacement coefficient based onlyon a shape of a histogram corresponding to a section that does notinclude the mode (frequency d3) in the shape of the histogram in FIG.8D.

Further, in the present modified example, calibrator 250 calculates thedisplacement coefficient by using the peak values of the histogram.However, calibrator 250 may calculate the displacement coefficient byusing other shape characteristics of the histogram. For example,calibrator 250 may use a position serving as a valley of the histogramas the shape characteristic of the histogram.

Second Exemplary Embodiment

Herein, a load meter according to a second exemplary embodimentconfigured by modifying a part of the configuration of load meter 200 inthe first exemplary embodiment will be described as one aspect of thepresent disclosure.

FIG. 9 is a view schematically illustrating one example of a state inwhich an axle load is measured according to the second exemplaryembodiment of the present disclosure. As illustrated in FIG. 9 , loadmeasuring system 2 according to the second exemplary embodiment includestwo load sensors 100 and load meter 201.

Load meter 200 in the first exemplary embodiment acquires a capturedimage from imaging device 101, and calculates a road surfacedisplacement, an axle number, and a speed from this image. On the otherhand, in load meter 201 in the second exemplary embodiment, asillustrated in FIGS. 9 and 10 , input unit 211 acquires an output valueof load sensor (a strain gauge, a piezoelectric element, or the like)100 installed in road 103. Load meter 201 detects a displacement amountfrom the output value of load sensor 100. Herein, as illustrated in FIG.9 , two or more load sensors 100 are installed adjacent to each other,and a positional relationship of load sensors 100 is already known.

Hereafter, a detail of this load meter 201 will be described withreference to the drawings, focusing on differences from load meter 200in the first exemplary embodiment.

[2-1. Configuration]

FIG. 10 is a block diagram illustrating a configuration of load meter201 in the second exemplary embodiment.

As illustrated in FIG. 10 , load meter 201 includes input unit 211, axleload calculator 241, and calibration device 301. Calibration device 301includes axle identifying unit 221, speed calculator 231, calibrator251, detector 263, storage unit 270, and notification unit 280.

As illustrated in FIG. 10 , load meter 201 is different from load meter200 (see FIG. 2 ) in the first exemplary embodiment in that input unit211 acquires the output value of load sensor 100.

Axle identifying unit 221 counts the number of axles from the number ofchanges in the output value of load sensor 100 acquired by input unit211 accompanied by passage of a vehicle. If a certain amount of time haspassed since the output of load sensor 100, axle identifying unit 221determines the passage of the vehicle. Similarly, speed calculator 231measures the changes in the output value of load sensor 100 acquired byinput unit 211 accompanied by the passage of the vehicle. Then, speedcalculator 231 calculates a speed of the vehicle by using a passage timebetween the plurality of load sensors 100 and a known installationdistance between load sensors 100. Instead of the displacement amount inthe first exemplary embodiment, calibrator 251 and storage unit 270 eachuse the output value of load sensor 100 acquired by input unit 211.Similarly, instead of the displacement amount in the first exemplaryembodiment, axle load calculator 241 calculates an axle load by usingthe output value of load sensor 100 acquired by input unit 211. Detector263 calculates a displacement amount from the output value of loadsensor 100.

[2-2. Operation]

Load meter 201 performs, as its characteristic operation, a secondmeasurement process configured by modifying a part of the firstmeasurement process in the first exemplary embodiment.

Specifically, the second measurement process is different from the firstmeasurement process in that a procedure of steps S10 to S30 in theflowchart of FIG. 4A in the first exemplary embodiment is omitted.Further, the second measurement process is different from the firstmeasurement process in that detector 263 treats an amount of change inthe output value of load sensor 100 as a displacement amount. Further,in step S120, axle identifying unit 221 identifies an axle number fromthe number of changes in the output value of load sensor 100. Further,in step S130, speed calculator 231 calculates a speed of the vehiclefrom a time difference of changes in the output values of the pluralityof load sensors 100 and the installation distance between load sensors100. The other operations are identical to the operations in the firstexemplary embodiment.

[2-3. Effects Etc.]

As described above, load meter 201 uses the output value obtained byload sensor 100. Although input information is different from the inputinformation in the first exemplary embodiment, calibrator 251 aggregatesthe output values of load sensor 100 accompanied by the passage ofordinary passing vehicles through the operation identical to theoperation in the first exemplary embodiment. With this configuration,calibration of load meter 201 can be automatically performed.Accordingly, cost and labor for maintenance and management of themeasuring system can be reduced.

Further, even when the calibration is not performed automatically,calibration device 301 can automatically determine timing to becalibrated. Accordingly, updating work can be performed in a necessaryand sufficient frequency.

Third Exemplary Embodiment

Herein, a load meter according to a third exemplary embodimentconfigured by modifying a part of the configuration of load meter 200 inthe first exemplary embodiment will be described as one aspect of thepresent disclosure.

FIG. 11 is a view schematically illustrating one example of a state inwhich load meter 202 according to the third exemplary embodimentmeasures an axle load of vehicle 102. As illustrated in FIG. 11 , loadmeasuring system 3 according to the third exemplary embodiment includesload meter 202 and imaging device 101. Load meter 202 includesinformation processor 320 and projector 310 for projecting patternedlight onto road 103. Also, imaging device 101 captures an image of road103 onto which the patterned light has been projected by projector 310.

Hereafter, a detail of this load meter 202 will be described withreference to the drawings, focusing on differences from load meter 200in the first exemplary embodiment.

[3-1. Configuration]

FIG. 12 is a block diagram illustrating a configuration of load meter202. As illustrated in FIG. 12 , in addition to input unit 210, axleload position identifying unit 261, storage unit 270, and axle loadcalculator 240 according to the first exemplary embodiment, load meter202 includes projector 310 and displacement amount detector 362according to the third exemplary embodiment.

Information processor 320 includes input unit 210, axle load positionidentifying unit 261, storage unit 270, axle load calculator 240, anddisplacement amount detector 362.

Projector 310 projects patterned light onto road 103. More specifically,projector 310 projects predetermined patterned light onto an areaincluding at least a part of an area included in a captured imagecaptured by imaging device 101, on a road surface of road 103.

Each of FIGS. 13A to 13E illustrates one example of patterned lightprojected onto road 103 by projector 310.

FIG. 13A illustrates an example of a case where patterned light 400A hasone line segment (line). FIG. 13B illustrates an example of a case wherepatterned light 400B has a plurality of (herein, three) line segments.FIG. 13C illustrates an example of a case where patterned light 400C hasone broken line (dots). FIG. 13D illustrates an example of a case wherepatterned light 400D has a plurality of (herein, three) broken lines.FIG. 13E illustrates an example of a case where patterned light 400E hasa checkered pattern.

Hereinafter, the patterned light projected onto road 103 by projector310 is described using patterned light 400A illustrated in FIG. 13A.However, a design of the patterned light may be any of patterned light400A to patterned light 400E illustrated in FIGS. 13A to 13E.Alternatively, the design of the patterned light is not limited to anyof these patterned light 400A to patterned light 400E, and any designmay be used. However, as described below, it is preferable that thepatterned light include a design having a line segment which is notsubstantially parallel to an imaging direction of a captured image.

FIG. 14 is a view schematically illustrating a relation between aprojecting direction of patterned light 400A projected by projector 310and an imaging direction by imaging device 101.

As illustrated in FIG. 14 , projector 310 and imaging device 101 aredisposed so that the projecting direction of patterned light 400A andthe imaging direction by imaging device 101 are not substantiallyparallel to each other. Specifically, a certain degree of angle (herein,for example, about 45 degrees) is formed between the projectingdirection of patterned light 400A and the imaging direction by imagingdevice 101.

In this example, patterned light 400A is a line segment extending in theprojecting direction. Accordingly, the angle is formed to prevent adirection of this line segment and the imaging direction by imagingdevice 101 from becoming substantially parallel to each other.

FIG. 15A is a view schematically illustrating patterned light 400A asseen in the imaging direction by imaging device 101 when an axle load isnot applied to road 103. FIG. 15B is a view schematically illustratingpatterned light 400A as seen in the imaging direction by imaging device101 when the axle load is applied to road 103.

As illustrated in FIG. 15B, when the axle load is applied to road 103,displacement occurs in a local area of road 103 to which the axle loadis applied (hereinafter also referred to as a “load local area”).Because of this, displacement also occurs in patterned light 400Aprojected in this load local area.

When the direction of the line segment of patterned light 400A in theload local area and the imaging direction are substantially parallel toeach other, it is difficult for the displacement of patterned light 400Ato appear as displacement on a captured image.

Therefore, it is desirable that the patterned light projected byprojector 310 have a line segment which is not substantially parallel tothe imaging direction by imaging device 101.

Returning to FIG. 12 again, and description of projector 310 iscontinued.

For example, projector 310 may include a laser light oscillator foroutputting laser light. In this case, patterned light is realized by thelaser light output from the laser light oscillator.

Further, projector 310 may include, for example, a light emitting diode(LED). In this case, patterned light is realized by light output fromthe LED.

Further, projector 310 may project patterned light by visible light ormay project patterned light by near infrared light if, for example, itis an electromagnetic wave in a frequency band that can be captured byimaging device 101.

Further, for example, projector 310 may receive a signal from a sensorfor sensing vehicle 102 traveling on road 103, and project patternedlight at a timing when vehicle 102 approaches an area onto whichpatterned light is projected. In this case, projector 310 generates atiming signal indicating a timing of projecting the patterned light, andtransmits the timing signal to imaging device 101. Also, imaging device101 may receive the timing signal, and capture an image at the timing ofprojecting the patterned light indicated by the timing signal. In thepresent disclosure, the sensor for sensing vehicle 102 may besubstituted for imaging device 101. Further, load measuring system 3 mayinclude the sensor for sensing vehicle 102 apart from imaging device101.

Further, imaging device 101 may receive the signal from the sensor forsensing vehicle 102 traveling on road 103, and capture a to-be-capturedimage at the timing when vehicle 102 approaches the area onto which thepatterned light is projected. In this case, imaging device 101 transmitsa timing signal indicating a timing of capturing the to-be-capturedimage to projector 310. Also, projector 310 may receive the timingsignal, and project patterned light at the timing of capturing theto-be-captured image indicated by the timing signal.

Further, projector 310 and imaging device 101 may receive the signalfrom the sensor for sensing vehicle 102 traveling on road 103. Projector310 projects patterned light at the timing when vehicle 102 approachesthe area onto which the patterned light is projected. Also, imagingdevice 101 may capture a to-be-captured image at the timing when vehicle102 approaches the area onto which the patterned light is projected.

Displacement amount detector 362 detects, by using a captured imagereceived by input unit 210, a displacement amount of patterned light, inthe captured image, corresponding to displacement caused on the roadwhen an axle load is applied. Particularly, when an axle load positionis input from axle load position identifying unit 261, displacementamount detector 362 detects a displacement amount corresponding todisplacement of patterned light at the identified axle load position. Bycomparing a captured image in which no displacement is caused on thepatterned light and a captured image in which displacement is caused onthe patterned light, from among a plurality of captured images receivedby input unit 210, displacement amount detector 362 detects adisplacement amount corresponding to the displacement. Displacementamount detector 362 can detect a displacement amount between thecaptured images by using block matching, a correlation method, or anoptical flow. For example, displacement amount detector 362 calculates,as the displacement amount, the number of pixels that indicates adifference in pixel positions corresponding to an identical point on theroad between the captured images. Further, the captured image in whichno displacement is caused on the patterned light may be a captured imagein which the road, onto which the patterned light has been projected, iscaptured in advance in a state in which the vehicle is not present, acaptured image in which an image change amount is less than or equal toa certain level among a plurality of captured images of the road, ontowhich the patterned light has been projected, captured in succession, ora captured image determined that the vehicle is not present through theimage recognition processing.

An operation of load meter 202 having the above-mentioned configurationwill be described with reference to the drawings hereafter.

[3-2. Operation]

Load meter 202 performs, as its characteristic operation, a thirdmeasurement process.

[3-2-1. Third Measurement Process]

The third measurement process is a process, when a captured imageincluding a vehicle is input to load meter 202, for calculating an axleload of the vehicle, and is a process configured by modifying a part ofthe first measurement process in the first exemplary embodiment.

FIG. 16 is a flowchart for describing the operation of the thirdmeasurement process.

As illustrated in FIG. 16 , the third measurement process is a processconfigured by modifying the process in step S30 of the first measurementprocess in the first exemplary embodiment to a process in step S330.Therefore, the process in step S330 will be mainly described herein.

Upon the identification of the axle load position in the process in stepS20, displacement amount detector 362 detects a displacement amount ofpatterned light corresponding to displacement caused at the identifiedaxle load position on road 103 (step S330). Displacement amount detector362 detects a displacement amount by using captured image A in whichdisplacement is caused on a patterned light and captured image B inwhich no displacement is caused on the patterned light. If capturedimage B has not been acquired by input unit 210 before the axle loadposition is identified, displacement amount detector 362 waits untilcaptured image B is acquired by input unit 210, and then detects thedisplacement amount.

FIG. 17 is a view illustrating one example of captured image A acquired.As illustrated in FIG. 17 , captured image A includes patterned light400A projected onto road 103 and vehicle 102 traveling on road 103.Also, this vehicle 102 is in contact with road 103 at lowermost point810 of a tire of vehicle 102. Further, patterned light 400A is projectedonto an area including lowermost point 810 of the tire and a local areaon road 103 near lowermost point 810.

FIG. 18 is one example of captured image B acquired. As illustrated inFIG. 18 , captured image B does not include a vehicle traveling on road103, while including patterned light 400A projected onto road 103.

Road 103 is imaged from an identical point of view (that is, a point ofview of imaging device 101) in captured image A and captured image B.Area 910 on road 103 in captured image B is an area identical to thearea on road 103, which corresponds to lowermost point 810 of the tire,in captured image A.

Displacement amount detector 362 detects a displacement amount ofpatterned light caused between an area on road 103, which corresponds tolowermost point 810, in captured image A, and area 910 in captured imageB.

After the process in step S330 is ended, the third measurement processproceeds to a process in subsequent step S40.

[3-3. Effects Etc.]

As described above, load meter 202 irradiates road 103 with patternedlight. Accordingly, on road 103 in which load meter 202 is installed,even if brightness of reflected light from a road surface under naturallight is flat, a difference of elevation is created on the brightness ofthe reflected light from the road surface by the patterned lightirradiated. Generally, a displacement amount in a captured image whosebrightness having a difference of elevation is detected more preciselythan a displacement amount in a captured image having flat brightness.

As a result, load meter 202 can measure an axle load of a vehicle stillmore precisely than a type of load meter that does not irradiate road103 with patterned light.

Further, as described above, load meter 202 measures an axle load of avehicle by utilizing reflected light from the road surface by thepatterned light irradiated.

As a result, load meter 202 can measure the axle load of the vehicleeven under an environment where a quantity of natural light isabsolutely small, such as at night, in the early morning, in theevening, or in bad weather.

Other Exemplary Embodiments

As described above, the first, second, and third exemplary embodimentshave been described as an illustration of the technique disclosed in thepresent application. However, the technique in the present disclosure isnot limited to those, and can be also applied to exemplary embodimentsin which changes, replacements, additions, omissions, or the like aremade as appropriate.

(1) The present disclosure has been stated that load meter 200 is anexample of the configuration provided with input unit 210 receiving aninput of a captured image of road 103 captured by imaging device 101.However, if load meter 200 can acquire the captured image, load meter200 is not necessarily provided with input unit 210. For example, loadmeter 200 may include an imaging unit for generating a captured image,instead of including input unit 210. Further, the captured image used byaxle load position identifying unit 261 may be a captured image capturedby the imaging unit. This configuration eliminates a need of theexternal imaging device.

(2) The present disclosure has been stated that load meter 200 is anexample of the configuration implemented in such a way that amicroprocessor in a computer provided with the microprocessor and amemory executes a program stored in the memory. However, if load meter200 has a function equivalent to the function in the above-describedimplementation example, load meter 200 is not necessarily limited to theconfiguration example implemented according to the above-describedimplementation example. For example, load meter 200 may be an example ofthe configuration in which a part of or all of components constitutingload meter 200 are implemented by a dedicated circuit.

(3) The present disclosure has been stated that load meter 200 is anexample of the configuration for recognizing a tire of a vehicle by animage processing and identifying an area on road 103 corresponding tothe lowermost point of the tire as an axle load position. However, themethod for identifying the axle load position is not necessarily limitedto the above-mentioned method. For example, load meter 200 may identifya position where a displacement amount locally becomes the maximum asthe axle load position.

(4) In the present disclosure, axle identifying unit 220 (one example ofa vehicle type recognition unit) may recognize a vehicle type from thecaptured image, and calibrator 250 may selectively generate a histogramfor a specific vehicle type. A shape characteristic of the histogram canbe easily obtained by selecting the vehicle type. Accordingly, thecalibration precision improves.

(5) In the present disclosure, detector 260 may calculate reliability ofthe displacement amount from the captured image. Further, calibrator 250may aggregate the displacement amounts and generate the histogram of thedisplacement amounts, only when the reliability is higher than apredetermined value. A correlation coefficient, sharpness ofdistribution of correlation functions, or the like, in case of using acorrelation method, can be used as the reliability. The calibrationprecision is improved by using a highly precise displacement detectionresult.

(6) In the present disclosure, a captured image may be a monochromeimage, a color image, or a multispectral image. In addition, light forcapturing an image may be ultraviolet rays, near infrared rays, or farinfrared rays, besides visible light.

(7) The present disclosure has been described by using an example of theasphalt-paved road surface as the road surface of road 103. However, theroad surface of road 103 may be, in addition to the asphalt-paved roadsurface, a road surface formed of another pavement material, such asconcrete. Further, the road surface of road 103 may be a road surface ofthe above-described paved road surface partially coated with a platematerial, a sheet material, a coating material, or the like. To moreprecisely and significantly obtain displacement based on an image, theroad surface of road 103 may be coated with one of the above-mentionedmaterials, and the coated area may be defined as an area from whichdisplacement is to be detected.

(8) The components (function blocks) in load meters 200, 201, 202 may beindividually implemented as a single chip, or a single chip may includea part of or all of the components, by means of a semiconductor device,such as an integrated circuit (IC) or large scale integration (LSI). Themethod of implementing integrated circuitry is not limited to the LSI,and implementation may be achieved by means of dedicated circuitry or ageneral-purpose processor. A field programmable gate array (FPGA) forwhich programming is possible after LSI fabrication, or a reconfigurableprocessor allowing reconfiguration of connections and settings ofcircuit cells within an LSI, may also be used. Further, when anintegrated circuit implementation technique comes out to replace the LSIas a result of the development of semiconductor technique or anothertechnique derived from the semiconductor technique, the function blocksmay be integrated by using that technique. For example, application ofbiotechnology is possible.

(9) All of or a part of various processes described above may beimplemented by a hardware product such as an electronic circuit, or maybe implemented by using software. It is to be noted that the processusing software is implemented in such a way that the processor in theload meter executes the program stored in the memory. Furthermore, theprogram may be recorded in a recording medium and may be distributed orcirculated. For example, the distributed program is installed in anotherdevice including a processor, and the program is executed by theprocessor. In this way, the device can execute the above-describedprocesses.

(10) The embodiments implemented by any combination of the componentsand functions of the above-mentioned exemplary embodiments are includedin the scope of the present disclosure.

(11) As illustrated in FIG. 14 in the third exemplary embodiment, thepresent disclosure has been stated that projector 310 is disposed sothat the projecting direction by projector 310 is not substantiallyparallel to the imaging direction of the captured image. However, thepresent disclosure is not limited to this. If a line segment of a designof patterned light projected by projector 310 is not substantiallyparallel to the imaging direction of the captured image, projector 310may be disposed so that the projecting direction by projector 310 isparallel to the imaging direction of the captured image. Specifically,projector 310 may be disposed directly above or directly below imagingdevice 101.

(12) As illustrated in FIG. 14 in the third exemplary embodiment, thepresent disclosure has been stated that the patterned light projected byprojector 310 includes the design having the line segment which is notsubstantially parallel to the imaging direction of the captured image.However, the present disclosure is not limited to this. If projector 310is disposed so that the projecting direction of projector 310 is notsubstantially parallel to the imaging direction of the captured image,the line segment of the design of the patterned light may be parallel tothe imaging direction of the captured image.

INDUSTRIAL APPLICABILITY

The load meter according to the present disclosure is widely applicableto a load meter for measuring a load.

REFERENCE MARKS IN THE DRAWINGS

-   -   1, 2, 3: load measuring system    -   100: load sensor    -   101: imaging device    -   102: vehicle    -   103: road    -   200, 201, 202: load meter    -   210, 211: input unit    -   220, 221: axle identifying unit    -   230, 231: speed calculator    -   240, 241: axle load calculator (load calculator)    -   250, 251: calibrator    -   260, 263: detector    -   261: axle load position identifying unit    -   262, 362: displacement amount detector (detector)    -   270: storage unit    -   280: notification unit    -   300, 301: calibration device    -   310: projector

The invention claimed is:
 1. A load meter comprising: a projectorconfigured to project patterned light onto a road; a detector configuredto detect, by using a captured image obtained by capturing an areahaving the patterned light projected onto the road and a vehicle presentin the area, a displacement amount of the patterned light in thecaptured image, the displacement amount corresponding to displacementcaused on the road by application of a load of the vehicle; a storageunit configured to store information indicating a relation between theload and the displacement amount; and a load calculator configured tocalculate the load based on the displacement amount and the information.2. The load meter according to claim 1, wherein the patterned lightincludes a design having a line segment that is not substantiallyparallel to an imaging direction of the captured image.
 3. The loadmeter according to claim 1, wherein the projector is disposed so that aprojecting direction by the projector is not substantially parallel toan imaging direction of the captured image.
 4. The load meter accordingto claim 1, wherein the projector generates a timing signal indicating atiming of projecting the patterned light, and the captured image is animage captured at the timing indicated by the timing signal.
 5. The loadmeter according to claim 1, wherein based on a signal from a sensor fordetecting the vehicle traveling on the road, the projector projects thepatterned light, and the captured image is captured.
 6. The load meteraccording to claim 1, further comprising a calibrator configured to:generate a histogram of a plurality of the displacement amounts byaggregating the displacement amounts detected by the detector, andupdate a displacement coefficient for calculating the load of thevehicle based on a shape of the histogram.
 7. The load meter accordingto claim 6, wherein the load of the vehicle is an axle load of thevehicle.
 8. The load meter according to claim 6, further comprising anaxle identifying unit configured to identify an axle number of an axleof the vehicle, wherein the calibrator generates the histogram for eachaxle number identified by the axle identifying unit, and updates thedisplacement coefficient based on the shape of the histogram.
 9. Theload meter according to claim 8, wherein the axle identifying unitidentifies a first axle serving as a forefront axle of the vehicle, andthe calibrator updates the displacement coefficient based only on theshape of the histogram corresponding to the first axle.
 10. The loadmeter according to claim 6, further comprising a speed calculatorconfigured to calculate a speed of the vehicle, wherein the calibratorgenerates the histogram for each speed calculated by the speedcalculator, and updates the displacement coefficient based on the shapeof the histogram.
 11. The load meter according to claim 6, furthercomprising a vehicle type recognizer configured to recognize a type ofthe vehicle, wherein the calibrator generates the histogram for eachtype recognized by the vehicle type recognizer, and updates thedisplacement coefficient based on the shape of the histogram.
 12. Theload meter according to claim 6, wherein the detector calculatesreliability of the displacement amount, and the calibrator aggregatesthe displacement amounts only when the reliability is higher than apredetermined value.
 13. The load meter according to claim 6, whereinthe calibrator updates the displacement coefficient based only on theshape of the histogram corresponding to a section that does not includea mode of the histogram.
 14. The load meter according to claim 6,wherein the calibrator updates the displacement coefficient only when apredetermined condition is satisfied.
 15. The load meter according toclaim 6, further comprising a notification unit, wherein thenotification unit performs notification when a difference between adisplacement coefficient before being updated by the calibrator and thedisplacement coefficient updated by the calibrator is a predeterminedreference value or more.
 16. The load meter according to claim 6,wherein the storage unit records a histogram of a plurality of theloads, and the calibrator updates the displacement coefficient based onthe shape of the histogram of the displacement amounts and a shape ofthe histogram of the loads.
 17. A load measurement method comprising:projecting patterned light onto a road; detecting with a detectorconfigured to detect an image, by using a captured image obtained bycapturing an area having the patterned light projected light onto theroad and a vehicle present in the area, a displacement amount of thepatterned light in the captured image, the displacement amountcorresponding to displacement caused on the road by application of aload of the vehicle; and calculating with a load calculator the loadbased on the displacement amount and information, stored in a storageunit, indicating a relation between the load and the displacementamount.
 18. The load measurement method according to claim 17, furthercomprising: generating a histogram of a plurality of the displacementamounts by aggregating the displacement amounts detected in thedetecting; and updating a displacement coefficient for calculating theload of the vehicle based on a shape of the histogram.